Development of Microelectromechanical Systems (MEMS) forceps for intraocular surgery

Compliant Cross-Axis Joints: A Tailoring Displacement Range Approach via Lattice Flexures and Machine Learning

Compliant joints are flexible elements that allow displacement due to the elastic deformations they experience under the action of external loading. The flexible parts responsible for these displacements are known as flexure hinges. Displacement, or motion range, in compliant joints depends on the stiffness of the flexure hinges and can be tailored through various parameters, including the overall dimensions, the base material, and the distribution within the hinge. Considering the distribution, we propose the stiffness modification of a compliant cross-axis joint via the use of lattice mechanical metamaterials. Due to the wide range of parameters that influence the stiffness of a lattice, different machine learning algorithms (artificial neural networks, support vector machine, and Gaussian progress regression) were proposed to forecast these parameters. Here, the machine learning algorithm with the best forecasting was the Gaussian progress regression; this algorithm has the advantage of well-tuning even with small regression databases, allowing these functions to more easily adjust to suit specific data, even if the dataset is small. Hexagonal, re-entrant, and square lattices were studied as flexure hinges. For each, the effect of the unit cell size and its orientation with respect to the principal axis on the effective stiffness were studied via computational and laboratory experiments on additively manufactured samples. Finite element predictions resulted in good agreement with the experimentally obtained data. As a result, using lattice-flexure hinges led to increments in displacement ranging from double to ten times those obtained with solid hinges. The most suitable machine learning algorithm was the Gaussian progress regression, with a maximum error of 0.12% when compared to the finite element analysis results.

Comparison of Anatomical and Functional Results of Surgeries Performed with Nitinol Flex Loop or Forceps in Primary Epiretinal Membrane

Purpose: To compare surgery's effect with nitinol flex loop (NFL) or forceps on retinal layers and functional outcomes in the primary epiretinal membrane (ERM).Methods: The operations were classified according to the use of the NFL or forceps. Automatic segmentation of the individual inner retinal layers was performed by spectral-domain optical coherence tomography software, and best-corrected visual acuity (BCVA) before surgery and at the last follow-up visit postoperatively were compared.Results: Forty-two eyes of 42 patients were included with a mean age of 66.9 ± 5.7 years. 45.2% of the surgeries were NFL assisted, 54.8% were forceps assisted. The mean follow-up duration was 9.8 ± 1.3 months. The mean BCVA was 0.79 ± 0.42 vs 0.77 ± 0.39 logMAR in the preoperative period and 0.42 ± 0.27 vs. 0.40 ± 0.21 logMAR at last follow-up in the NFL vs forceps group respectively (p= .403). The retinal nerve fiber layer (RNFL)(32.5% vs. 50.1%, p= .009), ganglion cell layer (18.1% vs. 41.4%, p= .021), inner plexiform layer (13.5% vs. 32.7%, p= .031) and inner nuclear layer (15.5% vs. 30.3%, p= .011) thickness decreased significantly more in the forceps group. The mean surgical time was not significantly different (45.2 ± 5.1 vs. 51.1 ± 6.1 minutes) in the NFL vs. forceps groups, respectively (p= .331).Conclusion: Following primary ERM surgery, the inner retinal layers become thinner; RNFL impacted the most, which was found higher in forceps assisted surgeries. This result shows that the NFL can be used safely in macular surgery.

Guided Electrokinetic Assembly of Polystyrene Microbeads onto Photopatterned Carbon Electrode Arrays

Assembly of microdevices from constituent parts currently relies on slow serial steps via direct assembly processes such as pick-and-place operations. Template Electrokinetic Assembly (TEA), a guided, noncontact assembly process, is presented in this work as a promising alternative to serial assembly processes. To characterize the process and its implementation of electrokinetic, dielectrophoretic, and electro-osmotic phenomena, we conducted studies to examine the assembly of polymer microparticles at specific locations on glassy carbon interdigitated electrode arrays (IDEAs). The IDEAs are coated with a layer of lithographically patterned resist, so that when an AC electric field is applied to the IDEA, microparticles suspended in the aqueous solution are attracted to the open regions of the electrodes not covered by photoresist. Interplay between AC electro-osmosis and dielectrophoretic forces guides 1 and 5 μm diameter polystyrene beads to assemble in regions, or "wells", uncovered by photoresist atop the electrodes. It was discovered that AC electro-osmosis under an applied frequency of 1 kHz is sufficient to effectively agglomerate 1 μm beads in the wells, whereas a stepwise process involving the application of a 1 MHz signal, followed by a 1 kHz signal, is required for the positioning of 5 μm beads, which are mainly affected by dielectrophoretic forces. Permanent entrapment of the microparticles is then demonstrated via the electropolymerization process of the conducting polymer polypyrrole.

Simulation, Fabrication and Analysis of Silver Based Ascending Sinusoidal Microchannel (ASMC) for Implant of Varicose Veins

Bioengineered veins can benefit humans needing bypass surgery, dialysis, and now, in the treatment of varicose veins. The implant of this vein in varicose veins has significant advantages over the conventional treatment methods. Deep vein thrombosis (DVT), vein patch repair, pulmonary embolus, and tissue-damaging problems can be solved with this implant. Here, the authors have proposed biomedical microdevices as an alternative for varicose veins. MATLAB and ANSYS Fluent have been used for simulations of blood flow for bioengineered veins. The silver based microchannel has been fabricated by using a micromachining process. The dimensions of the silver substrates are 51 mm, 25 mm, and 1.1 mm, in length, width, and depth respectively. The dimensions of microchannels grooved in the substrates are 0.9 mm in width and depth. The boundary conditions for pressure and velocity were considered, from 1.0 kPa to 1.50 kPa, and 0.02 m/s to 0.07 m/s, respectively. These are the actual values of pressure and velocity in varicose veins. The flow rate of 5.843 (0.1 nL/s) and velocity of 5.843 cm/s were determined at Reynolds number 164.88 in experimental testing. The graphs and results from simulations and experiments are in close agreement. These microchannels can be inserted into varicose veins as a replacement to maintain the excellent blood flow in human legs.

Design, Fabrication, and In Vitro Testing of an Anti-biofouling Glaucoma Micro-shunt

Glaucoma, one of the leading causes of irreversible blindness, is a progressive neurodegenerative disease. Chronic elevated intraocular pressure (IOP), a prime risk factor for glaucoma, can be treated by aqueous shunts, implantable devices, which reduce IOP in glaucoma patients by providing alternative aqueous outflow pathways. Although initially effective at delaying glaucoma progression, contemporary aqueous shunts often lead to numerous complications and only 50% of implanted devices remain functional after 5 years. In this work, we introduce a novel micro-device which provides an innovative platform for IOP reduction in glaucoma patients. The device design features an array of parallel micro-channels to provide precision aqueous outflow resistance control. Additionally, the device's microfluidic channels are composed of a unique combination of polyethylene glycol materials in order to provide enhanced biocompatibility and resistance to problematic channel clogging from biofouling of aqueous proteins. The microfabrication process employed to produce the devices results in additional advantages such as enhanced device uniformity and increased manufacturing throughput. Surface characterization experimental results show the device's surfaces exhibit significantly less non-specific protein adsorption compared to traditional implant materials. Results of in vitro flow experiments verify the device's ability to provide aqueous resistance control, continuous long-term stability through 10-day protein flow testing, and safety from risk of infection due to bacterial ingression.

Intraocular Microsurgical Forceps (20, 23, and 25 gauge) Membrane Peeling Forces Assessment

Background. To assess the peeling forces exerted by different calibers of microsurgical forceps on an experimental model of epiretinal membrane. Methods. A model of epiretinal membrane was constructed using thin cellulose paper and heptanes-isopropyl alcohol 1% mixture. The model was mounted on a force censoring device. Subsequently, flaps were created with three different microsurgical forceps of different calibers. We recorded the number of attempts, the duration of the event, and the pushing and the pulling forces during the peeling. The results were compared by a one-way ANOVA and a Fisher unprotected least significant difference test with an alpha value of 0.05 for statistically significance. Results. There was a statistical significant difference on the pulling and pushing forces between the 25 gauge (13.79 mN; -13.27 mN) and the 23 (6.63 mN; -5.76 mN) and 20 (5.02 mN; -5.30 mN) gauge, being greater in the first (P < 0.001). There were no differences in the duration of all events, meaning that all the forces were measured within the same period of time. Conclusions. The 25 gauge microsurgical forceps exerted the greatest mechanical stress over our simulated epiretinal membrane model and required more attempts to create a surgical suitable flap. The clinical implication of this finding is still to be determined.

Nanomedicine in ophthalmology: the new frontier

PURPOSE

To review the fields of nanotechnology and nanomedicine as they relate to the development of treatments for vision-threatening disorders.

DESIGN

Perspective following literature review.

METHODS

Analysis of relevant publications in the peer-reviewed scientific literature.

RESULTS

Nanotechnology involves the creation and use of materials and devices at the size scale of intracellular structures and molecules and involves systems and constructs on the order of <100 nm. The aim of nanomedicine is the comprehensive monitoring, control, construction, repair, defense, and improvement of human biological systems at the molecular level, using engineered nanodevices and nanostructures, operating massively in parallel at the single cell level, ultimately to achieve medical benefit. The earliest impact of nanomedicine is likely to involve the areas of biopharmaceuticals (eg, drug delivery, drug discovery), implantable materials (eg, tissue regeneration scaffolds, bioresorbable materials), implantable devices (eg, intraocular pressure monitors, glaucoma drainage valves), and diagnostic tools (eg, genetic testing, imaging, intraocular pressure monitoring). Nanotechnology will bring about the development of regenerative medicine (ie, replacement and improvement of cells, tissues, and organs), ultrahigh-resolution in vivo imaging, microsensors and feedback devices, and artificial vision. "Regenerative nanomedicine," a new subfield of nanomedicine, uses nanoparticles containing gene transcription factors and other modulating molecules that allow for the reprogramming of cells in vivo.

CONCLUSIONS

Nanotechnology already has been applied to the measurement and treatment of different disease states in ophthalmology (including early- and late-stage disease), and many additional innovations will occur during the next century.

BioMEMS -Advancing the Frontiers of Medicine

Biological and medical application of micro-electro-mechanical-systems (MEMS) is currently seen as an area of high potential impact. Integration of biology and microtechnology has resulted in the development of a number of platforms for improving biomedical and pharmaceutical technologies. This review provides a general overview of the applications and the opportunities presented by MEMS in medicine by classifying these platforms according to their applications in the medical field.

Microtechnologies in medicine: an overview

Microsystems technology (MST) has become a significant enabler of novel medical devices and implants over the last years. Typical examples are MST units in cardiac rhythm management devices or in hearing implants. A classification of medical MST applications can be made according to their relationship with the anatomy that is based on the kind and duration of interaction with the human body: Class 1: Extra-corporeal devices such as telemetric health monitoring systems or point of care testing systems. Class 2: Intra-corporeal devices such as intelligent surgical instruments. Class 3: Temporarily incorporated or ingested devices, such as telemetric endoscopes. Class 4: Long-term implantable devices such as telemetric implants. Medical applications of MST are growing at double-digit compounded growth rates, leading to a forecasted global market volume of over USD 1 billion in 2006 or 2007, making MST devices a relevant segment of the medical technology market. The clinical foundation for promoting the use of MST in medicine is mainly based on the significant potential of MST to enable products that improve early disease detection and the monitoring of chronic illnesses. This refers to a number of the most important health problems such as cardiovascular disease, hypertension, diabetes and cancer, to name just a few. More recently microrobotics has become a relevant research area for enabling the atraumatic transport of MST-enhanced diagnostic and therapeutic devices inside the human body.